black smoke

ok i have a 2004 yz 250f that hasent been riding in about 3 months due me being hurt and stuff. well when i started it today and reved it black smoke came out of the muffler. ONLY when i reved it. now is that due to the bike not being started in a long time or what.

o yea i did start the bike about a week ago and the same thing happen.

thanks mike

black smoke is rich mix, blue smoke is oil, white smoke is steam.

could be you gummed up the carb a bit and now its rich or the floats is a bit sticky. You can try throwing a bit of carb cleaner in the gas to help dissolve the gum. A bit mind you not a lot.

thanks im prop going to just take the carb off anyway and just clean it since i got 2 others carbs to take off anyway. my yz and my husky and my dads kdx.


did you ever fix the prop you were having with the 05 yz 450f yet

Did you warm it up completely. You should try riding it around for 10 or 15 minutes before you judge the mixture. Maybe the combustion chamber didn't come up to temp, and all the fuel in the mixture didn't remain vaporized. This could result in black smoke from an incomplete burn. Black smoke is unburnt fuel, and it generally means you are rich, as stated above, but I'd make sure it's warmed up completely before I judged the mixture.

If it only does it when you rev it up, it also might mean your AP squirt is too rich, depending on if you twisted the throttle quickly enough for the AP to be a factor.

yeh I have helped it a little bit so far. 13T counter sprocket, tossed the screen, cut the rear wall down in the airbox, a Ti-4 slip on and wrapped the exhaust in header wrap has gotten it to run comparable to the 250's now. It's not as quick yet, but I suspect the cdi unti will resolve that and make it quicker. The CDI unit that I had hoped to cure it's lazyass attitude was dead on arrival. I have another coming that should help it snap to attention for me. And of course if that doesnt work I can toss an overbore and a set of hotcams on it. He11 maybe a supercharger will get it to run as fast as my preconcieved dreams say it should. :cry:

However I have found the perfect use for the 450. I have found that since it's 12 pounds heavier and is harder to make turn, I have to ride much more aggressively on it to get the same feeling of ride. It really pumps up my guns so much that I can jump on the 250 and throw it around like a little biatch bike. And thats a really cool thing because I was thinking I was getting stagnant on the 250. ha! not even.

well it never did this before do you think it could be the cold weather making it rich.. ill first try cleaning the carb out then letting it fully warm up and see.


i heard that the 03 flywheel is 4or 5 ouces lighter than the 05 so i would do asking around on that... so taht might also help

cold air is denser and will make a bike leaner if it has the same jetting as it did when it was warmer temps. so somehow it's getting too much fuel. Or not enough air (main air jet or pilot jet plugged up)

As soon as they get the microfiche to show 05 part numbers at the shop it will show if the 05 has a different flywheel. It probably does, since I can putz around on it without any throttle and it wont stall.

I'm sure there's going to be a middle point where I am satisfied with it. I just wish it was as light and nimble as the 04 yz250f, but thats what the 06 450 will bring. :cry:

but thats what the 06 450 will bring.

yup im waiting for that one to :cry:

is the fuel stale and did you leave the feul turned on?

this can both do it,

black smoke is noting to worry about just let it warm up and ride

is the fuel stale and did you leave the feul turned on?

this can both do it,

nope the fuel was shut off but i think the gas is old

try just emptying the tank and carb and putting fresh fuel in.

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